“And that applies equally to boys, sir?”

“Yes,” Jack smiled.

“Do you consider yourself, sir, fully competent to handle this craft?”

“I’d rather someone else would say it,” Jack replied.  “My employers, though, seem to consider me competent.”

“What is this material, sir?” continued the cadet, resting a hand on a piston rod.

“Brass,” Benson replied, promptly.

“Do you know the specific gravity and the tensile strength of this brass?”

Before Jack could answer Mr. Mayhew broke in, crisply: 

“That will do, Mr. Merriam.  Your questions appear to go beyond the limits of ordinary instruction, and to partake more of the nature of a cross-examination.  Such questions take up the time of the instruction tour unnecessarily.”

Cadet Merriam flushed slightly, as he saluted the naval officer.  Then the cadet’s jaws settled squarely.  He remained silent.

A few more questions and the hour was up.

Lieutenant Commander Mayhew gave the order for the cadets to pass above and embark in the cutters.  He remained behind long enough to say to the three submarine boys: 

“You have done splendidly, gentlemen—­far better than I expected you to do.  If you manage the sea instruction as well, in the days to come, our cadets will have a first-class idea of the handling of the Pollard boats.”

“I wish, sir,” Jack replied, after thanking the officer, “that the cadets were not required to say ‘sir’ to us.  It sounds odd, and I am quite certain that none of the young men like it.”

“It is necessary, though,” replied Mr. Mayhew.  “They are required to do it with all civilian instructors, and it would never do to draw distinctions on account of age.  Yes; it is necessary.”

When the second squad of cadets arrived, in the afternoon, the three submarine boys found themselves ready for their task without misgivings.  Eph took more part in the explanations than he had done in the forenoon.  Then came a third squad of cadets, to be taken over the same ground.  The young men of both these squads used the “sir” at once, having been previously warned by one of the naval officers.

“That will be all for to-day, Mr. Benson, and thank you and your friends for some excellent work,” said Lieutenant Commander Mayhew, when the third squad had filed away.

“Say, for hard work I’d like this job right along,” yawned Eph Somers, when the three were alone in the cabin.  “Just talking three times a day—­what an easy way of living!”

“It’s all right for a while,” agreed Jack.  “But it would grow tiresome after a few weeks, anyway.  Lying here in the Basin, and talking like a salesman once in a while, isn’t like a life of adventure.”

“Oh, you can sigh for adventure, if you wish,” yawned Eph.  “As for me, I’ve had enough hard work to appreciate a rest once in a while.  Going into the town to-night, Jack?”